Medical errors in hospitals rank as the third leading cause of death in the United States, exceeded only by cancer and heart attacks, according to researchers at Johns Hopkins University. At least 200,000 preventable deaths occur annually in these institutions of healing, although some researchers say the true number may be double that. Hospital-acquired infections, diagnostic errors, and medication mix-ups are among the leading culprits. Data compiled on the Medicare.gov Hospital Compare website and by U.S. News and World Report are designed to help consumers make educated choices, but how reliable are their data? And can a troubled hospital turn itself around?